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Paul Davies raises a critical point on the paradoxical arrow of time ( 25 September, p 34 ). Surely, the process of measurement at the quantum level defines a direction of time. Indeed, one could also extend this to note that the discussion about the (theoretical) reversibility of gas mixing is dependent upon perfect knowledge …

You wonder why orcas have started ramming boats off Gibraltar ( 18 September, p 17 ). Has any thought been given to the possibility that these animals may be perceiving the boats as competitors for the tuna they eat and are attempting to drive them away?

You report work on the viability of life that relies on photosynthesis in the sheltered zone of caves on Mars ( 4 September, p 9 ). As life has evolved to process energy from chemosynthesis on Earth, surely life on Mars is more likely to exist without any need for photosynthesis, especially given the proportionate …

David Hambling's interesting article on firing weapons from autonomous warships mentioned that any strike from an uncrewed ship mandated human control ( 18 September, p 11 ). Given that the last drone strike in Afghanistan was planned and executed by humans, resulting in the deaths of 10 civilians (seven of whom were children), maybe it …

In one part of your illuminating article on a net-zero life, you mention the fictional Isla planning a holiday that avoids the "moral opprobrium" of long-haul flights in favour of a train tour in Norway ( 4 September, p 34 ). While I agree that travelling by train is preferable to flying within Europe, I …

Your article missed a vital aspect of our transport future. A person on a pedal bike is the most efficient form of transport, as defined by distance travelled per unit of energy consumed. An extra bonus could be added to this equation if the person eats a plant-based diet. Plants fuelling bicycle transport is the …

Heat pumps probably are the way forward, especially in new-build homes. However, in existing housing, the payback time is long. And like many green technologies, the first things the user will notice are a rise in both installation and running costs over the status quo, an increase in noise and a decrease in convenience. Heat …

Some will say that using AI to identify targets for military strikes is a dangerous step down the road to mechanised, dehumanised warfare ( 2 October, p 14 ). Others will say that having two parallel decision processes, AI and human, will reduce, though not eliminate, error. Yet others will say that no targeting can …

Questions about such use of AI are raised by Arthur Holland at the UN Institute for Disarmament Research. He asks whether, in the case of an erroneous target selection, the use of AI might "affect the balance of human responsibility and accountability". I find this troubling because the question itself suggests we are yet again …

The experiments cited in your entertaining article on spite could cut two or more ways ( 4 September, p 40 ). For example, in the Ultimatum Game, the potential spitefulness of the "receiver" is considered in a one-play, known-rules, sharing game, yet the possible spitefulness of the "giver" goes unremarked. Why is it spiteful to …